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Biology > Biological molecules 2.1.2 Carbohydrates > Flashcards

Biological molecules 2.1.2 Carbohydrates Flashcards

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1
Q

Monosaccarides and diasaccarides

A

A monosaccaride is a single sugar unit e.g. glucose, fructose and ribose. When 2 monosaccarides link together they form a diasaccaride e.g. lactose and sucrose. When two or more monosaccarides are linked it forms a polysaccaride e.g. glycogen, cellulose and starch.

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2
Q

Monosaccarides

A

Monomer of carbohydrates, they are sugars, have the general formula (CH2O)n where n is either 3 5 or 6. Contain the functional group OH and dissolve in water

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3
Q

When n = 3

A
  • The formula would be C3 H6 O3
  • The sugar is called triose
  • Triose phosphate = sugar involved in respiration and photosynthesis.
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4
Q

When n=5

A
  • The formula would be C5 H10 O5
  • Sugar is called pentose
  • e.g. ribose in RNA, ATP and deoxyribose in DNA
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5
Q

The structure of ribose

A

*Look at powerpoint

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6
Q

When n=6

A
  • The formula would be C6 H12 O6
  • Sugar is called hexose
  • e.g. glucose transports sugar in animals and the main respiratory substrate
  • Fructose, found in plant transport sugar
  • Galactose found in milk sugar
  • All hexoses are structural isomers (same chemical formula but different molecular structure)
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7
Q

Structure of alpha glucose

A
  • look on power point
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8
Q

Structure of beta glucose

A

*look on power point

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9
Q

Glucose molecules

A

They are polar and soluble in water due to the hydrogen bonds that form between the hydroxl groups and the water molecules. The solubility id important because it means glucose is dissolved into the cytosol of the cell.

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10
Q

Difference between alpha and beta glucose

A
  • For alpha the -OH on c1 is below the plane of the ring and on the same side as the -OH on c4
  • For beta -OH on c1 is above the ring and the opposite side to -OH on c4
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11
Q

Ribose

A

Number of carbons = 5
Number of carbons in ring = 4
Type of ring = 5 membered
Oxygen atom present in ring? = yes
Chemical formula = C5 H10 O5

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12
Q

Glucose

A

Number of carbons = 6
Number of carbons in ring = 5
Type of ring = 6 membered
Oxygen atom present in ring? = yes
Chemical formula = C6 H12 O6

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13
Q

Fructose

A

Number of carbons = 6
Number of carbons in ring = 4
Type of ring = 5 membered
Oxygen atom present in ring? = yes
Chemical formula = C6 H12 O6

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14
Q

Diasaccarides

A
  • 2 monosaccarides joined together by a condensation reaction

General formula = (C6 H12 O6)2 - H2O= C12 H22 O11

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15
Q

Maltose

A
  • Present in germinating seeds
  • Function = source of energy for germination
  • Structure = look on powerpoint
  • The bond formed between 2 monosaccarides is a glycosidic bond
  • Disaccarides can be broken by a hydrolysis reaction
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16
Q

Sucrose

A
  • Transport sugar in the phloem
  • Composed of alpha glucose and fructose
  • a non reducing sugar
  • see on pp for structure
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17
Q

Lactose

A
  • Milk sugar
  • Composed of glucose and beta galactose
  • Joined together by a a beta 1,4 glycosidic bond (the glucose and galactose are flipped with respect to eachother)
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18
Q

Polysaccarides

A
  • Polymer of carbohydrates
  • Long chain of carbohydrate molecules made up of condensed monosaccarides
    -There are 3 common types which are all polymers of glucose (C6 H12 O6)
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19
Q

General formula of polysaccarides

A

(C6 H10 O5)x + (H2O)
where x = number of monomers in the chain.

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20
Q

Starch

A
  • Function molecule in plants
  • Source of glucose/ energy for respiration
  • Insoluble so does not affect water potential of the cell
  • Found in chloroplasts, amyloplasts
  • Storage organs: tubers(for asexual reproduction), seeds (grain, following sexual reproduction).
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21
Q

Amylose (structure)

A
  • 20% of starch
  • Monomer = alpha glucose
  • Bonds = alpha 1,4 glycosidic bonds
  • Structure = Helical molecule, helix held together by intramolecular H molecules.
  • Mr = 50000
  • About 300 glucose residues in a molecule of amylose
  • Look at structure on pp
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22
Q

Amylopectin

A
  • 80% of starch
  • monomer = alpha glucose
  • Mr = 500000
  • About 3000 glucose residules in a molecule of amylopectin
  • Bonds = 1,4 and 1,6 glycosidic bonds
  • Structure = branched
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23
Q

Iodine entering starch

A

Iodine ions enter the helix and absorb light of a different wavelength turing starch blue/black. Heat breaks the hydrogen bonds and iodine is released so blue/black colour dissapears.

24
Q

Glycogen

A
  • Storgae carbohydrate found in animal cells
  • Monomer is alpha glucose
  • Structure = highly branched
  • Bonds = alpha 1,4 and 1,6 glycosidic bonds
  • Upto 60000 glucose residues in a molecule of glycogen
25
Q

Why are glycogen and amylopectin good energy stores?

A

They are compact, insoluble and branched

26
Q

What are the advantages of glycogen and amlylopectin being branched?

A
  • Many glucose monomers available at branch endings which allows rapid release of glucose for respiration to provide energy for the cell.
27
Q

What are the advantages of glycogen and amlylopectin being compact?

A
  • Many glucose monomers exist in a small volume so large quantities of energy can be stored in the cell
28
Q

What are the advantages of glycogen and amlylopectin being insoluble?

A
  • They do not affect water potential so do not cause osmotic swell.
29
Q

Comparison of glycogen and amylopectin

A

-Glycogen is more highly branched than amylopectin so more glucose monomers are hydrolysed e.g. more rapid release for glucose for animals which are more metabolically active than plants.
- Glycogen is more insoluble then starch as it is larger.

30
Q

Cellulose (what is the monomer, structure?)

A
  • Component of plant and algae cell walls
  • Monomer = beta glucose
  • Structure = linear
  • About 10000 glucose molecules in a chain
  • Bonds = beta 1,4 glycosidic bonds
31
Q

Why does cellulose not coil?

A
  • THe chain does not coil because each beta glucose monomer is 180 degrees/upside down opposite orientation with respect to it’s neighbour
  • Each chain lies parallel to the next and can form hydrogen bonds with it.
32
Q

Reason and significance for cellulose being insoluble

A
  • Very large polymer with many H bonds keeping strands together so no access for water molecules to bond with polar OH groups
33
Q

Reason and significance for cellulose being flexible

A
  • Bundles of cellulose chains (microfibrils) can slide against eachother when the cell has to stretch or bend
34
Q

Reason and significance for cellulose having high tensile strength

A
  • Many intermolecular H bonds between the individual cellulose molecules within the microfibrils hold the chains firmly together
35
Q

Reason and significance for cellulose being unreactive

A

Glucose monomers held in a chain (plus many H bonds between cellulose molecules) which are not easily hydrolysed to be available for respiration

36
Q

Reason and significance for cellulose being linear

A

Beta glucose monomers flip 180 degrees alternately giving rise to strands which are parallel to eachother

37
Q

Reason and significance for cellulose being unbranched

A

Only beta 1,4 glycosidic bonds between the beta glucose monomers present (no 1,6)

38
Q

Macrofibrils in cellulose

A
  • Formed from the hydrogen bonding of about 80 molecules of cellulose together
  • Runs in a lot of directions giving plant cell walls extra support
39
Q

Cellulose fibres in plant cell

A

Cellulose fibres stop the plant cell from bursting when it is turgid, this turgidity gives the plant tissue support and strength.

40
Q

Chitin

A
  • A polysaccaride
  • Cell wall of fungi and exoskeleton of arthropods
41
Q

Benedicts test for reducing sugars

A
  • Heat and add glucose to Copper sulphate (Cu 2+ in CuSO4, appears as a blue solution is benedicts solution)
  • Cu 2+ –> Cu+ (red ppt)
  • Positive test for reducing sugar = brick red precipitate
  • As temp increases the colour changes from blue to green to yellow to orange to red.
  • All sugars are reducing EXCEPT for sucrose
42
Q

Benedicts test for non-reducing sugars

A
  • Sucrose is a non reducing sugar so it must be hydrolysed to fructose and glucose before giving positive test for benedicts
    The test involves 3 steps:
    1. Heat sucrose and add HCL (hydrolysis)
    2. Neutralise the pH by adding NaHCO3
    3. Heat with benedicts
43
Q

Why does sucrose need to be treated to have a positive benedicts test result?

A

Untreated sucrose is a disaccaride which cannot donate molecules due to glycosidic bonds between monomers, so benedicts solution will remain blue. The acid and heat hydrolyses the sucrose into glucose and fructose which are reducing sugars.

44
Q

Why is HCL added to sucrose in benedict test?

A

To neutralise the pH as the reaction requires alkaline conditions.

45
Q

What is a colorimeter?

A

A colorimeter is used to determine how much light a solution absorbs. Colorimetry involves the use of a colorimeter, a device that detects how much light is absorbed by the solution. In other words, how much of the light that is travelling through the solution is being stopped by the solution.

46
Q

What occurs when sucrose is broken down to monosaccharides?

A

hydrolysis, releasing reducing sugars and using water

47
Q

What is the specific, full name for the bond that joins glucose molecules to start a new branch in amylopectin and glycogen?

A

Alpha (1,6)

48
Q

Which structure is formed from several adjacent cellulose molecules hydrogen bonding with each other?

A

Microfibril

49
Q

What is the transport carbohydrate in animals?

A

glucose

50
Q

What sugars are found in sucrose?

A

sucrose = glucose + fructose
maltose = glucose + glucose
Lactose = Glucose + galactose

51
Q

Which molecule consists of many alpha glucose molecules joined together by alpha (1-4) glycosidic bonds only?

A

Amylopectin

52
Q

What is the specific, full name for the bond that joins glucose molecules into a chain in cellulose?

A

beta (1,4) glycosidic bonds

53
Q

Which structure is formed from several adjacent cellulose macrofibrils binding with each other?

A

A cellulose fibre

54
Q

Which disaccharide is the transport carbohydrate in plants?

A

sucrose

55
Q

Which bonds bind one cellulose molecule to adjacent cellulose molecules to create a microfibril?

A

hydrogen bonds

56
Q
A

Biology (5 decks)

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